Drifters may be used to track currents in a moving liquid, such as the ocean. To maximize tracking accuracy, a drifter may be designed to maximize drag, particularly in a horizontal direction. This may be accomplished by making the drifter in a shape with a large frontal area when viewed from any lateral direction. The large frontal area creates a large drag that resists motion of the drifter through the liquid so that the drifter accurately moves with the current. A large submerged drag area also minimizes the influence of unwanted motion induced by other factors such as the force of wind on parts of the drifter exposed above the surface. An ocean drifter may be passive, without means for self-propulsion.
On the other hand, self-propelled vehicles, such as boats or autonomous underwater vehicles (AUVs), may be designed to minimize drag so that they can travel efficiently through the liquid. This may be particularly important for battery-powered vehicles for which energy may be limited, and in which drag may directly impact travel speed and total travel distance. A primary way to minimize drag on a device is to minimize its frontal area. AUVs may be a means for gathering oceanographic data. Such vehicles may be used to carry sensors and imaging equipment. However, a low-drag vehicle may be ill-suited for the high-drag requirement of a device for gathering accurate drift measurements. Thus, there is a need for a device that has the mobility of a vehicle and the accurate current measurement capability of a drifter.